η the viscosity of the fluid. We also have the following equality: Ut = (τ/ρ)1/2 which yields after solving for τ: τ = Ut2*ρ After equating the two expressions for τ and some rearrangements one arrives at an expression for the crosswise spacing λ: λ = 100*(η/ρ)*(8/Um2*f)1/2 By inserting the following realistic values one finds for λ: η = 1.06*10−3 [Pa*s] ρ = 1000 [kg/m3] f = 0.01 Um = 1 [m/s] λ = 100*1.06*10−6*(800)1/2 = 1.06*10−4*28.28 λ = 2.998*10−3 [m] The calculated crosswise spacing λ is 3 millimeters. This value is in fairly close agreement with the experimental values measured by Allen, which are nevertheless generally 2 to 4 times higher. The discrepancy can be explained by assuming that only strongly developed streaks leave a discernible ridge. Conclusions Parting lineation is a very good indicator of the reigning current direction (and therefore also a good paleocurrent indicator). An analysis of the grain fabric furthermore leads to the determination the younging direction within the sedimentary succession. The lower part of the upper plane bed hydraulic regime of relatively swift currents is characterized by parting lineation. References Sedimentary structures